The disclosure of Japanese Patent Application No. HEI 11-99251 filed on Apr. 6, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a vehicle control apparatus having a power source and a continuously variable transmission that is capable of continuously changing the speed transfer ratio and a vehicle control method. More particularly, the invention relates to a control apparatus that performs a control to reduce front-rear vibrations of a vehicle occurring, for example, at the time of a state change of the vehicle from a decelerating state to an accelerating state, and a vehicle control method.
2. Description of the Related Art
It is known that the body of a vehicle having a continuously variable transmission experiences a front-rear vibration at the end of a speed shift to a higher speed transfer ratio of the continuously variable transmission that is performed on the basis of an acceleration request or an output power increase request made by, for example, a depression of an accelerator pedal or the like. Such vibration, generally termed bucking or transient surge, is caused by inertia torque, an elasticity of a power transmitting system, and the like. More specifically, when the speed transfer ratio of the continuously variable transmission is increased upon an acceleration request or an output increase request to the power source such as an engine or the like, the rotational speed of a rotating body involved in power transmission changes, thereby producing inertia torque in accordance with the amount of rotational speed change of the rotating body (angular acceleration) and the inertia moment. The inertia torque is released when the rotational speed of the rotating body stabilizes at a target speed, that is, approximately at the time of the end of the speed shift. As a result, the released inertia torque temporarily increases the driving torque, so that a front-rear vibration occurs due to the deflection elasticity of the power transmission system.
Japanese Patent Application Laid-Open No. HEI 11-5460 describes a control apparatus for reducing transient surges as described above. The control apparatus calculates a half period of a transient surge (vehicle front-rear vibration) that is expected to occur at the end of a speed shift, on the basis of the output torque of the engine and the speed transfer ratio of the continuously variable transmission. Between the time point preceding the end of the speed shift by the half period of the vehicle front-rear vibration and the end of the speed shift, the control apparatus sets the torque provided for the wheel side to a half of a target torque. Subsequently, the control apparatus increases the torque to the target torque in a stepped manner. As a result, during the duration between the time point preceding the end of the speed shift by the half period and the end of the speed shift, about half the inertia torque is released. After the speed shift ends, the remaining inertia torque is released in the form of a vibration whose phase is opposite to that of the vehicle front-rear vibration, so that the inertia torque offsets the vehicle front-rear vibration. In this manner, the control apparatus reduces transient surges.
However, the control performed by the above-described control apparatus is a theoretical control based on an ideal model in which no backlash or the like exits in the drive power transmitting system including the differential device and the like. In reality, a vehicle has a great number of non-linear factors (e.g., impacts caused by backlashes of gears, splines, and the like of the drive power transmitting system). Backlashes in the drive power transmitting system have great effect, particularly when the power transmitting state changes from a driven state in which the power source side (including the engine, the continuously variable transmission and the like) is driven by wheels connected to the continuously variable transmission to a driving state in which the output of the power source side is transmitted to the wheel and therefore drives the wheels. The kinetic energy stored by movements in backlash is instantly transferred at the sites of impacts at the change from the aforementioned driven state to the aforementioned driving state. Corresponding to the impacts, the transmission timing of the output of the power source side deviates. Therefore, even if the above-described transient surge-reducing control apparatus is applied to an actual vehicle, there occur impacts at unintended timings, deviation of the timing of the vibration reducing control, and the like, so that the control apparatus fails to sufficiently reduce the vehicle front-rear vibrations. As a result, an occupant in the vehicle is occasionally annoyed or discomforted. A control apparatus disclosed in Japanese Patent Application Laid-Open No. HEI 11-33613 avoids backlash movements, if any backlash space exits, by adjusting the torque output of the power source side or the torque adjusting control duration in such a direction as to fill in or eliminate the backlash spaces. After eliminating the backlash spaces, the control apparatus performs a control of reducing a transient surge as described above. Therefore, the control apparatus is able to effectively reduce the vehicle front-rear vibrations.
However, at the time of the start of the above-described backlash-reducing control, a relative movement between the power source side and the wheel side is started and, therefore, an inertia torque is produced. Therefore, the control apparatus described in Japanese Patent Application Laid-Open No. HEI 11-33613 cannot fully establish the state of the ideal model assumed in Japanese Patent Application Laid-Open No. HEI 11-5460, so that the application of the above-described theoretical control results in insufficient reduction of vehicle front-rear vibrations. Thus, the control apparatus described in Japanese Patent Application Laid-Open No. HEI 11-33613 still has a problem of annoying or discomforting an occupant in the vehicle in a subtle but unignorable manner.
Accordingly, it is an object of the invention to provide a control apparatus and a control method for a vehicle having a power source and a continuously variable transmission wherein even if a backlash-reducing control and a transient surge-reducing control are performed in combination, the transient surge-reducing control can be effectively performed to further reduce vibrations of the vehicle.
To achieve the aforementioned and other objects, one aspect of the invention provides a vehicle control apparatus including a power source, and a continuously variable transmission capable of continuously varying a speed transfer ratio. When the power source and the continuously variable transmission change from a driven state to a driving state with respect to a wheel side, the vehicle control apparatus performs a backlash-reducing control that substantially eliminates a backlash present in a power transmitting system so as to reduce a vibration of a vehicle caused by the backlash, and subsequently performs a transient surge-reducing control that increases, in a stepped manner, a control torque applied to the wheel side so as to reduce the vibration of the vehicle by controlling an output torque of the power source and the speed transfer ratio of the continuously variable transmission based on a natural vibration frequency of the vehicle. In that case, the vehicle control apparatus sets an initial control duration of the transient surge-reducing control following the backlash-reducing control to a duration that is shorter than a half of a natural vibration period of the vehicle, based on a control amount of the backlash-reducing control.
Another aspect of the invention provides a vehicle control apparatus including a power source, and a continuously variable transmission capable of continuously varying a speed transfer ratio. When the power source and the continuously variable transmission change from a driven state to a driving state with respect to a wheel side, the vehicle control apparatus performs a backlash-reducing control that substantially eliminates a backlash present in a power transmitting system so as to reduce a vibration of a vehicle caused by the backlash, and subsequently performs a transient surge-reducing control that increases, in a stepped manner, a control torque applied to the wheel side so as to reduce the vibration of the vehicle by controlling an output torque of the power source and the speed transfer ratio of the continuously variable transmission based on a natural vibration frequency of the vehicle. In that case, the vehicle control apparatus sets the control torque applied during an initial performance of the transient surge-reducing control following the backlash-reducing control to a value that is smaller than xc2xd of a desired target torque by a predetermined amount, based on a control amount of the backlash-reducing control. The control torque is then increased to the target torque in a stepped manner.
The aforementioned xe2x80x9cbacklashxe2x80x9d is a clearance provided for force-transmitting gear or spline portions. The size of each backlash provided at various sites is known at the time of designing a power transmitting system. The aforementioned xe2x80x9celiminates a backlashxe2x80x9d means that a clearance between tooth faces of gear or spline portions in a force-transmitting direction is gradually reduced until they contact each other, so as to avoid impactive collision between the tooth faces, for example, when the power source and the continuously variable transmission change from the driven state to the driving state with respect to the wheel side. The xe2x80x9ctransient surge-reducing controlxe2x80x9d is is a control that releases the inertia torque in a stepped manner and produces a vibration that has a phase opposite to that of the transient surge and therefore cancels out the transient surge by increasing the torque of the drive wheels in a stepped manner through control of the output torque of the power source and the speed transfer ratio of the continuously variable transmission.
The vehicle control apparatus as described above reduces the control amount (torque or control duration) applied for the transient surge-reducing control in accordance with the control amount provided by the backlash-reducing control. More specifically, the apparatus reduces the control amount of the transient surge-reducing control by an amount corresponding to a relative movement between the power source side and the wheel side that has already started, so as to utilize an extraneous amount of torque provided by the backlash-reducing control as a part of the transient surge-reducing control. In this manner, the control amount of the transient surge-reducing control is corrected as a whole to an appropriate value, so that front-rear vibrations of the vehicle can be favorably reduced or restrained.
A vehicle control method according to still another aspect of the invention includes a backlash-reducing control step of, when the power source and the continuously variable transmission change from a driven state to a driving state with respect to a wheel side, substantially eliminating a backlash present in a power transmitting system so as to reduce a vibration of the vehicle caused by the backlash, and a step of, subsequently to the backlash-reducing control step, increasing, in a stepped manner, a control torque applied to the wheel side so as to reduce the vibration of the vehicle by controlling an output torque of the power source and the speed transfer ratio of the continuously variable transmission based on a natural vibration frequency of the vehicle, during a duration that is set based on a control amount of the backlash-reducing control and that is shorter than a half of a natural vibration period of the vehicle.
A vehicle control method according to a further aspect of the invention includes a backlash-reducing control step of, when the power source and the continuously variable transmission change from a driven state to a driving state with respect to a wheel side, substantially eliminating a backlash present in a power transmitting system so as to reduce a vibration of the vehicle caused by the backlash, a torque setting step of, subsequently to the backlash-reducing control step, setting a torque that is produced by controlling an output torque of the power source and the speed transfer ratio of the continuously variable transmission based on a natural vibration frequency of the vehicle and that is applied to a wheel side, to a value that is smaller than xc2xd of a desired target torque by a predetermined amount, based on a control amount of the backlash-reducing control, and a step of, at least a predetermined length of time following the torque setting step, increasing the control torque applied to the wheel side to the target torque in a stepped manner.
Therefore, in a case where a backlash-reducing control that substantially eliminates a backlash present in a power transmitting system so as to reduce or restrain a vibration of a vehicle caused by the backlash is followed by a transient surge-reducing control that increases, in a stepped manner, a control torque applied to the wheel side so as to reduce the vibration of the vehicle by controlling an output torque of the power source and the speed transfer ratio of the continuously variable transmission, based on a natural vibration frequency of the vehicle, the method is able to utilize the inertia torque produced during the backlash-reducing control as a part of the transient surge-reducing control so as to effectively perform the transient surge-reducing control. Hence, the vibration of the vehicle can be further reduced.